The Moon lacks a true atmosphere because its gravity is too weak to hold gases for long. Any atoms released by radioactive decay, solar wind impacts, or micrometeorites quickly escape into space. What remains is called an exosphere. Atoms rarely collide with each other there. Each particle follows its own lonely arc. This makes the Moon an extreme vacuum environment.
This matters because surface conditions are harsh and unprotected. Radiation, temperature swings, and micrometeorites hit without resistance. Human exploration must compensate for this exposure.
It also explains why footprints last so long. With no wind or weather, the surface barely changes. The Moon preserves history in dust.
The Moon’s exosphere is billions of times thinner than Earth’s atmosphere. You couldn’t breathe even a single molecule of it.
NASA [nasa.gov]